In the field of manufacturing integrated circuits, miniaturization of processing size in the lithography process has continuously proceeded in order to attain higher integration degree and, in recent years, technology enabling such fine processing of the order of sub-micron has been being developed. In such lithography process, a resist composition is coated on a substrate. The coating is then exposed using an exposure apparatus through a mask pattern to create a latent image of the mask pattern, and the latent image is developed using a proper developing solution to obtain a desired resist pattern. However, many of such substrates used have such a high reflectivity that, particularly when substrates with uneven surface are used, an exposure radiation having passed through the resist layer is reflected by the substrate to the resist layer again, thus problems of reflection notching, standing wave or dimensional unevenness of resulting resist pattern being caused.
In order to solve the problems, various methods have so far been investigated. For example, there are illustrated a method of dispersing or dissolving in the photoresist a dye having absorption at the wavelengths of exposure radiation (U.S. Pat. No. 4,882,260) and a method of absorbing exposure radiation having reached to the substrate by an anti-reflective layer formed on the substrate. As the latter method of forming an anti-reflective layer on the substrate, there have been known a method of forming an inorganic compound layer on a substrate by vacuum deposition, CVD method or the like (C. Nolscher, et al., Proc. SIPE, 1086, p. 242 (1989); K. Bather, et al., Thin Solid Films, 200, p. 93 (1991); and G. Czech, et al., Microelectronic Engineering, 21, p. 51 (1993)), a method of coating an organic polymer solution containing dissolved or dispersed therein a dye, a method of forming an anti-reflective layer by using a polymer dye wherein chromophores are chemically bonded to a polymer or using a polymer which itself has radiation absorbing property, and like method. These methods of using radiation absorbing polymers and radiation absorbing polymer materials for the methods are described in, for example, Japanese Unexamined Patent Publication Nos. H6-75378 and H6-118656, WO 9412912, U.S. Pat. Nos. 4,910,122 and 5,057,399, etc.
In forming the above-described organic anti-reflective coating, a photoresist-coating apparatus is often employed also as an apparatus for applying the anti-reflective coating composition. It is also desired in view of managing waste liquor that a solvent to be used for the anti-reflective coating composition be the same as that for the photoresist composition. However, in the case of forming the anti-reflective coating and the resist layer by using mutually the same solvent, intermixing between the anti-reflective coating and the resist layer is liable to take place upon applying a resist composition onto the anti-reflective coating already formed. In order to prevent this intermixing, it is necessary to introduce thermally cross-linkable properties into the anti-reflective coating. However, with some kinds of cross-linking agents to be used, the resist layer is adversely affected by the anti-reflective coating material containing the cross-linking agent to suffer footing or generation of scum, deformation of resist image, etc., thus failing to form a resist image with desired resolution and shape. In particular, where chemically amplified resists adapted for exposure radiation sources such as KrF excimer laser are used, the resists are liable to be adversely affected by the properties of anti-reflective coating, in particular, by acidic degree. Thus, improvement of the anti-reflective coating has been desired. In addition, in some cases, shape of resist pattern is changed in the interface between the resist and the anti-reflective coating depending upon the properties of the anti-reflective coating itself such as acidic degree. That is, with alkaline anti-reflective coating, tailing of a resist pattern is observed, whereas with acidic anti-reflective coating, resist pattern having undercut structure is formed. Thus, there has been desired an anti-reflective coating exerting less influences on a resist pattern.
An object of the present invention is to provide a coating composition which shows high anti-reflective properties, causes no intermixing upon applying thereon a resist, and causes no adverse influences on the shape of resist pattern and a method for forming a resist pattern using an anti-reflective coating having a proper acidic degree.